1. Field of the Invention
The present invention relates to an improvement in a recording method and recording apparatus for thermal transfer recording utilizing thermal recording head or the like.
2. Description of the Prior Art
There is known prior art of recording method, wherein recording medium and a transfer sheet comprising a base film on one face thereof having recording material such as ink to be transferred are provided, and by selectively raising temperature of the recording material by selective heating means or the like at a state of pressing the recording material, the recording material is transferred onto the above-mentioned recording medium to make recording.
In such kind of the conventional transfer recording, the recording is carried out in such a manner that melting point of at least one component material in the layer of the above-mentioned recording material is selected lower than a raised temperature, and by means of melting thereof the transfer is made on the recording medium. As representative recording apparatus, there is a thermal melting transfer recording apparatus wherein recordings of characters, figures or pictures are made by constituting the recording material from a colorant such as dye or pigment and binder of a low melting point and etc., and by making a transfer sheet of a so-called wax-type transfer sheet, made by coating the above-mentioned on a face of a heat resistive base sheet, such as thin capacitor paper or polyethylenetelephthalate sheet, and contacting a thermal recording head having a resistor element as heating points, the heat production being electrically controlled on the rear face of the transfer sheet, and selectively melting the binder through the base sheet by heating of the heater element, and thereby transferring the recording material on the recording medium such as paper.
In such kind of conventional recording apparatus, since the recording material media is heated from the rear face side of the base film, the melting starts from the contacting interface of the side of the base film, and only after melting of the side of the recording medium, the melted recording material is transfer-recorded on the face of the recording medium. Accordingly, since the transferring is carried out with outside heat energy of a value above a predetermined level to enable transfer, with a threshold level to produce incontinuous optical density of the recorded pattern, the conventional process can record only dual level optical density of recording without halftone gradation. Therefore, the conventional electric ink recording system has had a difficulty in reproducing picture having halftone optical density of the recording as its intrinsic problem.
Accordingly, in the conventional recording apparatus of thermal fusing type, in order to fulfil the present day's expanding needs for multi-gradation or continuous tone recording, optical density pattern process, dither process, digital gradation processing making multi-gradation recording with dual level optical density recoring, etc., are being studied.
In order to adopt such kind of multi-gradation or continuous tone recording, however, complicated signal processing circuit is usually needed, and the recording apparatus becomes expensive. Furthermore, the resolution of picture or recording speed decreases in inverse proportion to number of dots of the dual optical density recording in the matrix in dither process. The above-mentioned conventional multi-gradation recording methods are representing the optical density by number of dots in unit area. And accordingly, though they are multi-gradation recording, they can not produce image of continuous analog optical density in principle.
Furthermore, since the conventional thermal melting transfer recording apparatus controls heating of resistor element by current therein, its power consumption is large in comparison with its transferring capability, and a high speed recording is difficult. The breakthrough of the above-mentioned various problems have been subject of the technical study of the transfer recording.